Re: [PATCH for 6.0 v3] hw/intc/i8259: Refactor pic_read_irq() to avoid uninitialized variable

[Christian Borntraeger]

On 18.03.21 17:30, Philippe Mathieu-Daudé wrote:
> Some compiler versions are smart enough to detect a potentially
> uninitialized variable, but are not smart enough to detect that this
> cannot happen due to the code flow:
>
> ../hw/intc/i8259.c: In function ‘pic_read_irq’:
> ../hw/intc/i8259.c:203:13: error: ‘irq2’ may be used uninitialized in this 
> function [-Werror=maybe-uninitialized]
>     203 |         irq = irq2 + 8;
>         |         ~~~~^~~~~~~~~~
>
> Restrict irq2 variable use to the inner statement.
>
> Fixes: 78ef2b6989f ("i8259: Reorder intack in pic_read_irq")
> Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
 Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>

> ---
> Since v2:
> - Remove pic_intack() call (Zoltan)
> ---
>   hw/intc/i8259.c | 12 ++++++------
>   1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/hw/intc/i8259.c b/hw/intc/i8259.c
> index 344fd04db14..cc4e21ffec0 100644
> --- a/hw/intc/i8259.c
> +++ b/hw/intc/i8259.c
> @@ -176,10 +176,12 @@ static void pic_intack(PICCommonState *s, int irq)
>   int pic_read_irq(DeviceState *d)
>   {
>       PICCommonState *s = PIC_COMMON(d);
> -    int irq, irq2, intno;
> +    int irq, intno;
>   
>       irq = pic_get_irq(s);
>       if (irq >= 0) {
> +        int irq2;
> +
>           if (irq == 2) {
>               irq2 = pic_get_irq(slave_pic);
>               if (irq2 >= 0) {
> @@ -189,20 +191,18 @@ int pic_read_irq(DeviceState *d)
>                   irq2 = 7;
>               }
>               intno = slave_pic->irq_base + irq2;
> +            pic_intack(s, irq);
> +            irq = irq2 + 8;
>           } else {
>               intno = s->irq_base + irq;
> +            pic_intack(s, irq);
>           }
> -        pic_intack(s, irq);
>       } else {
>           /* spurious IRQ on host controller */
>           irq = 7;
>           intno = s->irq_base + irq;
>       }
>   
> -    if (irq == 2) {
> -        irq = irq2 + 8;
> -    }
> -
>   #ifdef DEBUG_IRQ_LATENCY
>       printf("IRQ%d latency=%0.3fus\n",
>              irq,